1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that is adaptive for driving a plurality of liquid crystal display panels by use of one backlight, thereby securing the mobility of a liquid crystal display panel and reducing its weight as well as its manufacturing cost.
2. Description of the Related Art
Generally, a liquid crystal display (hereinafter referred to as “LCD”) is on a broadening trend in its application scope due to its characteristic of lightness, thinness, low power consumption drive and so on. According to the trend, the liquid crystal display device is used in office automation OA equipment, audio/video equipment and so on. On the other hand, the liquid crystal display device controls the transmissivity of light beam in accordance with a video signal applied to a plurality of control switches that are arranged in a matrix shape, thereby displaying a desired picture on a screen.
The liquid crystal display device is not a self-luminous display device, thus it requires a light source like a backlight. The backlight for the liquid crystal display is divided into a flat type and an edge type. The flat type backlight has a plurality of lamps arranged in a plane in order to illuminate a large-sized or middle-sized liquid crystal display panel with light. And, a diffusion panel is installed between a fluorescent lamp and the liquid crystal display panel, and the gap between the liquid crystal display panel and the diffusion panel is maintained to be uniform. The edge type backlight has a lamp installed at the outer part of flat panel in order to illuminate a large-sized or middle-sized liquid crystal display panel with light, wherein the light generated from the lamp is incident to the entire surface of the liquid crystal display panel by use of a transparent light guide panel
Referring to FIG. 1, an edge type liquid crystal display device according to the related art includes a liquid crystal-display panel 2, a backlight unit to illuminate the liquid crystal display panel 2 with light, a support main 16 to have the backlight unit put therein, and a case top 6 to encompass the edge of the liquid crystal display panel 2 and the side wall of the support main 16.
The liquid crystal display panel 2 has liquid crystal cells arranged in an active matrix shape between an upper glass substrate and a lower glass substrate, and a thin film transistor is installed in each liquid crystal cell to switch video signals. The refractive index of each liquid crystal cell is changed in accordance with the video signal, thereby displaying a picture corresponding to the video signal. In this way, a tape carrier package (not shown), where a driver IC for applying drive signals to the thin film transistor is mounted, is stuck onto the lower substrate of the liquid crystal display panel 2. Also, polarizing sheets 8, 18 are each installed in the front and rear surfaces of the liquid crystal display panel 2. Herein, the polarizing sheets 8, 18 have a function of improving the viewing angle of the picture displayed by the liquid crystal cells.
The backlight unit includes a lamp 36 to receive power from an external power source and illuminate the liquid crystal display panel 2 with light; a light guide panel 12 to make the light progress toward the liquid crystal display panel 2, wherein the light is incident through a light entering part formed at the side surface opposite to the lamp 36; a lamp housing 34 to cover the lamp 36 as well as the light entering part of the light guide panel 12; a reflecting sheet 14 arranged at the rear surface of the light guide panel 12; a plurality of optical sheets 10 to improve the efficiency of the light coming out of the light guide panel 12, thereby illuminating the liquid crystal display panel 2 therewith.
The lamp 36 includes a high voltage electrode and a low voltage electrode formed at both ends of a glass tube, a high voltage wire 44 connected to the high voltage electrode by soldering, and a low voltage wire 42 connected to the low voltage electrode by soldering. Herein, the electrodes soldered with the wires 42, 44 are covered with an insulating holder.
The lamp housing 34 increases the efficiency of the light being incident from the lamp 36 and prevents the loss of light.
The light guide panel 12 has a designated tilt angle to guide the light incident from the lamp 36 to the liquid crystal display panel 2. At this moment, the reflecting sheet 14 makes the light generated from the lamp 36 guided to the light guide panel 12, and prevents the light loss generated from the lamp 36.
The optical sheets 10 makes the light incident slantingly from the surface of the light guide panel 12 vertically progress toward the liquid crystal display panel 2. In other words, the optical sheets 10 act to raise the propagation direction of the light up from the surface of the optical sheets 10.
The case top 6 is manufactured to have a shape of square belt with an orthogonally bent plane surface and side surface parts. The case top 6 encompasses the edge of the liquid crystal display panel 2 and the side surface of the support main 16.
The support main 16 is a mold of plastic material and its inner side wall is formed to be a stepped face. The backlight unit and the liquid crystal display panel 2 are deposited in the stepped face of the support main 16.
Herein, the illuminating method of the light generated from the backlight unit of FIG. 1 is described in detail.
Firstly, the lamp 36 receives power through the wires 42, 44 to generate light. The light from the part of the lamp facing the light entering part of the light guide panel 12 is directly incident to the light guide panel 12; and the light irradiated out from the side surface and the rear surface of the lamp 36 on the basis of the light entering part of the light guide panel 12 is reflected by the inner wall of the lamp housing 34 (which covers the lamp 36) and is incident to the light guide panel 12. The linear light incident to the light guide panel 12 in this way, as shown in FIG. 2, is converted into a surface light source while passing through the light guide panel 12 to be putting out to the liquid crystal display panel 2. At this moment, the light being leaked to the rear surface of the light guide panel 12 is reflected by the reflecting sheet 14 and is deposited in the rear surface of the light guide panel 12 to be incident to the light guide panel 12 again.
Next, the light coming out of the light guide panel 12 is irradiated onto the liquid crystal display panel 2 through the optical sheets 10. The upper and lower surfaces of the display panel 2 have the polarizing sheets 8, 18, attached thereto. Herein, the optical sheets 10, as shown in FIG. 2, include diffusion sheets 10A, 10B to diffuse the light coming out of the light guide panel 12 in order for the diffused light to be irradiated onto the liquid crystal display panel 2 in an average brightness; and prism sheets 10C, 10D to receive the diffused light from the diffusion sheets 10A, 10B and to make the light go out vertically to the liquid crystal display panel 2.
The light irradiating method of the backlight unit of the edge type liquid crystal display device according to the related art requires a combination of the light guide panel 12 and the lamp housing 34 fixed to prevent the leakage of the light generated from the lamp 36. Thus there is a problem in that the light source cannot have mobility. Also, in order to drive the liquid crystal display panel 2, there is required the backlight unit that irradiates light onto the liquid crystal display panel 2. Accordingly, the liquid crystal display device that drives the liquid crystal display panel has a problem in that there is a burden in weight as well as in cost due to the installation of the backlight unit.